Conventionally, an oil quenching type of cooling apparatus or a gas quenching type of cooling apparatus is used in cases in which high-speed cooling is required in a heat processing apparatus that performs processing such as quenching in which a treatment object in the form of a metal material is heated and then cooled. These oil quenching cooling apparatuses have superior cooling efficiency, however, they have the problem that they are substantially unable to perform precise cooling control and it is easy for an article being heat-treated to become deformed. In contrast, in gas quenching cooling apparatuses, although cooling control is easily achieved by controlling the gas flow rate so that these apparatuses less likely deform the article being heat-treated, they have the problem that they have inferior cooling efficiency.
Consequently, a technology is disclosed in Patent document 1 in which liquid nozzles and gas nozzles are disposed around an article being heat-treated, and cooling liquid is supplied as a spray from the liquid nozzles (what is known as mist cooling), while cooling gas is supplied from the gas nozzles. As a result, an improvement is achieved in both cooling controllability and cooling efficiency.